Nanotube relay device

ABSTRACT

The present invention relates to a nanotube device ( 100, 600 ), comprising a nanotube with a longitudinal and a lateral extension, a structure for supporting at least a first part of the nanotube, and first means for exerting a force upon the nanotube in a first direction defined by its lateral extension. At least a second part of the nanotube protrudes beyond the support of said structure, so that when said force exceeds a certain level, the second part of the nanotube will flex in the direction of its lateral extension, and thereby close a first electrical circuit. Suitably, the first means for exerting said force upon the nanotube is an electrical means, the force being created by applying a voltage to the means.

TECHNICAL BACKGROUND

Nanotechnology is a rapidly growing field of technology, including thedevelopment of so called nanotubes. Due to the inherently small size ofthe devices involved in this field of technology, nanotechnology wouldbe ideal for applications within for example the field of electronics,for example within the semiconductor field. Memory devices are oneexample of an application which would benefit greatly fromnanotechnology.

SUMMARY OF THE INVENTION

There is thus a need for a device in the nanoscale size which couldserve as a multi-state logical switch or a memory element.

This need is met by the present invention in that it provides a nanotubedevice comprising a nanotube with a longitudinal and a lateralextension, a structure for supporting at least a first part of thenanotube, and first means for exerting a force upon the nanotube in afirst direction defined by its lateral extension. At least a second partof the nanotube protrudes beyond the support of said structure, so thatwhen said force exceeds a certain level, the second part of the nanotubewill flex in the direction of its lateral extension, and thereby close afirst electrical circuit.

Suitably, the first means for exerting said force upon the nanotube isan electrical means, the force being created by applying a voltage tothe means.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below, with reference tothe appended drawings, in which:

FIG. 1 shows a schematic side view through a device according to theinvention, and

FIG. 2 shows a circuit equivalent to the device of FIG. 1, and

FIG. 3 shows current as a function of voltages in the device of FIG. 1,and

FIG. 4 shows an on-off transition for the current in the device in FIG.1, and

FIG. 5 shows a top view of an alternative embodiment of the invention.

EMBODIMENTS

FIG. 1 shows a first embodiment of a device 100 according to theinvention. The device comprises a nanotube 120, preferably a conductingnanotube, suitably a carbon nanotube.

The device further includes a structure 130, made of a non-conductingmaterial such as for example silicon, Si, which supports at least afirst portion of the nanotube, with another second portion of thenanotube protruding beyond the supporting structure, and thus beingunsupported. The first, supported, portion of the nanotube is connectedto an electrode 110, referred to from now on as the source electrode.

The supporting structure 130 is suitably shaped as a terrace, and thushas a “step-like” structure, with an upper level 130″, and a lower level130′, where the two levels are interconnected by a wall-like shape ofthe structure 110. The difference in height between the two levels 130′,130″ of the structure as defined by the height of the wall is referredto by the letter h. It should be noted that the use of the word “level”throughout this description refers to a difference in dimensions whichgives the structure a preferably step-like form either in the horizontalor in the vertical orientation of the device.

On the lower level 130′ of the structure, there are arranged twoadditional electrodes, one being referred to as the gate electrode 140,and the other as the drain electrode, 150. The gate electrode is locatedat a distance L_(G) to the nearest point of the wall, and thecorresponding distance for the drain electrode is denoted as L_(D),where L_(G) suitably is smaller than L_(D).

The total extension of the protruding part of the nanotube is preferablywithin the interval of 50 to 150 nm, suitably of the order ofapproximately 100 nm, with the height h being approximately in the orderof size of 3 nm.

When a voltage is applied to the gate electrode 140, a resultingcapacitive force will act on the nanotube 120, in the direction towardsthe gate electrode, which is thus a direction defined by the lateralextension of the nanotube, in the picture perceived as a “downwards”direction. The force, denoted as Fc, may be described by themathematical formula seen below:${Fc} = {{{- \left( {Q_{G}^{2}/2} \right)}\frac{\mathbb{d}}{\mathbb{d}x}\left( {1/{C_{G}(x)}} \right)} - {\left( {Q_{D}^{2}/2} \right)\frac{\mathbb{d}}{\mathbb{d}x}\left( {1/{C_{D}(x)}} \right)}}$

In this formula, Q_(G)+Q_(D) is the excess charge on the nanotube, C_(G)and C_(D) are capacitances which will be explained in more detail belowwith reference to FIG. 2, and x is the shortest distance between thenanotube 120 and the lower level 130′ of the structure.

FIG. 2 is an equivalent circuit 200 of the device in FIG. 1: The sourcevoltage V_(S) is connected, via an impedance Z, to the gate voltageV_(G) through the capacitance C_(G), and to the drain voltage V_(D)through the capacitance C_(D) and a resistance R_(T), which is connectedin parallel to the drain capacitance C_(D). Due to the mechanicalmovement caused by the force F_(C), the capacitances C_(G) and C_(D) andthe resistance R_(T) will vary in time.

The resistance R_(T) can be expressed by the formula seen below:R _(T) =R ₀ e ^(((h−x)/λ))

R₀ is estimated from experimental results, and can be said to be of theorder of tens to hundreds of kiloohms, and the tunneling length, λ, istypically in the order of 0.5 Å. The distance x can, as will berealized, be varied by varying the voltage V_(G) applied to the gate.

FIG. 3 shows the current-voltage function for a typical set ofparameters. On one of the horizontal axes, the gate voltage, V_(G) isshown, and on the other horizontal axis the drain voltage, V_(D), can beseen, with the vertical axis depicting the current which passes throughthe source electrode to the drain electrode. As can be seen from thisfigure, there is a sharp transition from a non-conducting (off) statefor the device to a conducting (on) state when the gate voltage isvaried, with the source voltage fixed.

FIG. 4 shows the current-voltage characteristics of the device with thesource voltage at a fixed value. The shift in gate voltage required tomake a transition from the “off” to the “on” state is approximately 1.5mV.

The time required to make a transition from the “on”-state to the“off”-state for the device in FIG. 1 is considerably much shorter thanthe time to make the opposite transition, i.e. from the “off”-state tothe “on”-state. Naturally, the switching dynamics of the deviceaccording to the invention can be affected by altering the geometry ofthe device, e.g. the wall height h, the positioning L_(G), L_(D) of theelectrodes on the lower level 130′ of the terrace, and the length of theprotruding part L of the nanotube. Thus, by suitable design, the deviceaccording to the present invention can be applied to meet the demands ofdifferent applications.

FIG. 5 shows a top view of another embodiment 500 of the invention. Thisembodiment 500 comprises a nanotube device similar to that shown in FIG.1 and described above, but with the supporting terraced structure 530additionally comprising a structure 530″ on a third level, said thirdlevel 530″ being located essentially in parallel with the second level530′, but on an opposite side of the protruding part of the nanotube520.

The embodiment 500 comprises essentially all of the features of thedevice in FIG. 1, and additionally comprises second means 540′ forexerting a force upon the nanotube 520 in a second direction defined byits lateral extension, so that when said force exceeds a certain level,the second part of the nanotube will flex in the second direction of itslateral extension, and thereby close a second electrical circuit. Saidsecond direction is, as will be realized from FIG. 5, the directionwhich is towards the means 540′. When force is exerted upon the nanotube520 via the means 540′, which is preferably a second gate electrode, thesecond, protruding, part of the nanotube 520 will flex in the seconddirection of its lateral extension, and thereby close a secondelectrical circuit. This second electrical circuit is suitably definedby the source electrode 510 described in connection with FIG. 1, and asecond drain electrode 550′ located on the third level 530″ of thesupporting structure 530.

The second gate and drain electrodes are located at distances L_(G2) andL_(D2) respectively from the wall of the terraced structure.

Although the invention has been described with reference to examples ofcertain embodiments, the invention may be varied within the scope of theappended claims.

1. A nanotube device (100,600), comprising a nanotube with alongitudinal and a lateral extension, a structure for supporting atleast a first part of the nanotube, and first means for exerting a forceupon the nanotube in a first direction defined by its lateral extension,characterized in that at least a second part of the nanotube protrudesbeyond the support of said structure, so that when said force exceeds acertain level, the second part of the nanotube will flex in thedirection of its lateral extension, and thereby close a first electricalcircuit.
 2. A nanotube device according to claim 1, characterized inthat the first means for exerting said force upon the nanotube is anelectrical means, the force being created by applying a voltage to themeans.
 3. A nanotube device according to claims 1 or 2, in which saidsupporting structure comprises a terraced structure with structures on afirst and a second level, with the supported first part of the nanotubebeing supported by the first level of the structure, and said means forexerting force being located on said second level.
 4. A nanotube deviceaccording to any of claims 1-3, in which the first means for applyingforce comprises a first gate electrode, and the first circuit which isclosed by the flexing of the nanotube comprises a first gate electrodebeing located on said second level of the structure and a first sourceelectrode being located on said first level of the structure.
 5. Ananotube device according to any of the previous claims, in which thesupporting terraced structure additionally comprises a structure on athird level, said third level being located essentially in parallel withsaid second level but on an opposite side of the protruding part of thenanotube, which nanotube device comprises second means for exerting aforce upon the nanotube in a second direction defined by its lateralextension, so that when said force exceeds a certain level, the secondpart of the nanotube will flex in the second direction of its lateralextension, and thereby close a second electrical circuit.
 6. A nanotubedevice according to claim 5, characterized in that the second means forexerting said force upon the nanotube is an electrical means, the forcebeing created by applying a voltage to the means.
 7. A nanotube deviceaccording to claims 5 or 6, in which said additional supportingstructure comprises a terraced structure with structures on a first anda second level, with the supported first part of the nanotube beingsupported by the first level of the structure, and said means forexerting force being located on said second level.
 8. A nanotube deviceaccording to any of claims 5-7, in which the second means for applyingforce comprises a second gate electrode, and the second circuit which isclosed by the flexing of the nanotube comprises a second drain electrodebeing located on said third level of the structure.